Anterior temporal lobe mediates associative and taxonomic neighborhood effects in lexical processing

Processing a word's meaning activates some of its semantic neighbors that are related associatively or taxonomically. While prior studies have shown that both types of neighborhoods influence lexical processing, their underlying neural bases remain unclear, particularly regarding the involvement of the Anterior Temporal Lobe (ATL). This study used HD-tDCS to examine the role of the left lateral ATL in how associative and taxonomic semantic neighborhoods influence the lexico-semantic processing of abstract and concrete words. Participants (N = 42) performed a semantic concreteness judgment task on words, with and without left ATL stimulation, where neighborhood sizes were varied. A strong facilitative effect of concreteness was found in both real and sham conditions, consistent with the traditional concreteness effect. Both associative and taxonomic semantic neighborhoods influenced semantic judgments. Critically, ATL stimulation slowed responses to words with sparse neighborhoods, regardless of whether neighborhoods were defined associatively or taxonomically. Furthermore, the neighborhood effects were more readily apparent for abstract words, with significant interactions between stimulation and neighborhoods observed only in this subset. Together, the findings highlight the independent effects of associative and taxonomic neighborhoods in lexico-semantic processing and show that the ATL modulates the activation of both associative and taxonomic semantic neighborhoods, challenging models that characterize it solely as a taxonomic hub.